A number of systems have been suggested for sensing the temperature within a refrigerated trailer and providing an output dependent upon the temperature within the trailer.
U.S. Pat. No. 4,024,495, for example, discloses a remote temperature-warning system for refrigerated vehicles that uses the existing electrical wiring of the vehicle. A visual temperature indicator is installed within the cab of the tractor to allow the driver to continuously monitor the temperature within the refrigerated compartment. An audio alarm is activated when the temperature measured within the refrigerated compartment exceeds a predetermined temperature.
U.S. Pat. No. 4,385,289 discloses a system for sensing the temperature within a refrigerated trailer and actuating an alarm when the temperature exceeds a preselected temperature. This system includes a control for switching between off, test and alarm modes of the system.
U.S. Pat. Nos. 3,363,231; 3,594,752; and 4,455,096 are directed to other devices for sensing the temperature within a tractor/trailer.
A number of systems have also been disclosed for sensing the distance between a vehicle and other objects. For example, U.S. Pat. No. 3,226,627 discloses a system to indicate the presence of an object and the distance between the object and the vehicle when the vehicle is being backed. The system uses sonar devices and presents the distance data by energizing a light bulb which flashes intermittently to indicate the distance between the vehicle and an object.
U.S. Pat. No. 3,681,750 discloses an ultrasonic vehicle detection device for indicating the presence of other vehicles in blind zones rearward of the vehicle. The apparatus of U.S. Pat. No. 3,681,750 includes a signal lamp to indicate the presence of a vehicle in such areas.
U.S. Pat. No. 3,732,555 discloses a radar system for aiding and maneuvering a truck at an unloading platform by operating a signal light to indicate to the driver that the truck is within a predetermined distance, for example, two to four feet of the loading dock as the vehicle is being backed.
U.S. Pat. No. 4,240,152 also discloses a system for locating and determining the distance of an object from a vehicle to avoid collisions during movement of the vehicle under low-overhanging structures. The system of U.S. Pat. No. 4,240,152 includes ultrasonic transmitters and receivers and a digital readout for indicating the distance of the vehicle from an object and warning devices for warning of an imminent collision. U.S. Pat. No. 4,240,152 indicates that the system may measure the distance of objects in front of or on top of the vehicle.
U.S. Pat. Nos. 3,226,673; 3,442,347; 3,360,775; 3,842,396; 4,015,232; 4,349,823; 4,442,512; 4,467,313; 4,528,563; and 4,694,297 also disclose systems to detect and warn the driver of objects within a predetermined distance of the vehicle.